C# Assert
last modified February 15, 2025
In this article, we show how to use the Assert class in C#. The
Assert class is part of the System.Diagnostics
namespace and is used for debugging and testing to validate conditions. If a
condition is not met, the Assert method throws an exception,
helping you identify issues in your code.
The Assert class is particularly useful for unit testing and
debugging, as it allows you to verify assumptions and catch errors early in the
development process.
Basic Usage of Assert
The following example demonstrates how to use the Assert class to
validate a condition.
int x = 10;
int y = 20;
// Assert that x is less than y
Debug.Assert(x < y, "x should be less than y");
Console.WriteLine("Assertion passed.");
In this program, the Debug.Assert method is used to validate that
x is less than y. If the condition is false, the
program will throw an exception with the specified message.
$ dotnet run Assertion passed.
If the condition is not met, the program will output:
$ dotnet run Debug Assertion Failed: x should be less than y
Assert with Custom Message
The following example demonstrates how to use the Assert class with
a custom error message.
int age = 15;
// Assert that age is greater than or equal to 18
Debug.Assert(age >= 18, "Age must be at least 18");
Console.WriteLine("Assertion passed.");
In this program, the Debug.Assert method is used to validate that
age is greater than or equal to 18. If the condition is false, the
program will throw an exception with the specified message.
$ dotnet run Debug Assertion Failed: Age must be at least 18
Assert with Complex Conditions
The following example demonstrates how to use the Assert class with
complex conditions.
string name = "Alice";
int length = name.Length;
// Assert that the name is not null and has a length greater than 0
Debug.Assert(!string.IsNullOrEmpty(name) && length > 0, "Name must not be null or empty");
Console.WriteLine("Assertion passed.");
In this program, the Debug.Assert method is used to validate that
name is not null or empty and has a length greater than 0. If the
condition is false, the program will throw an exception.
$ dotnet run Assertion passed.
Disabling Assertions
By default, assertions are only active in debug builds. To disable assertions,
you can define the DEBUG constant or use the
Conditional attribute. The following example demonstrates how to
disable assertions.
#define DEBUG // Comment this line to disable assertions
using System.Diagnostics;
int x = 10;
int y = 5;
// Assert that x is less than y
Debug.Assert(x < y, "x should be less than y");
Console.WriteLine("Assertion passed.");
In this program, the DEBUG constant is defined to enable
assertions. If you comment out the #define DEBUG line, assertions
will be disabled, and the program will not throw an exception.
$ dotnet run Debug Assertion Failed: x should be less than y
Source
In this article, we have shown how to use the Assert class in C#
for debugging and testing. The Assert class is a powerful tool for
validating conditions and catching errors early in the development process.
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